Electric discharge apparatus



Aug. 17, 1943. H. c. JENKS 2,327,268

ELECTRI C DI S CHARGE APPARATUS Filed Au '11, 1959 4 Sheets-Sheet 2 93f5 T 89 .9/ g

v I v 35.9 3 63 36/ 365 WITNESSES: INVENTOR 5% Hare/0 C. Jf/JKS.

Aug. 17, 1943. c. JENKS ELECTRIC DISCHARGE APPARATUS Filed Aug. 11, 19394 Sheets-Sheet 3 WWW INVENTOR fiar0/aCk/7K5.

' T To NEY WITNESSES:

Aug. 17, 1943. H. c. JENKS 3 ELECTRIC DISCHARGE APPARATUS Filed Aug. 11,1939 4 Sheets-Sheet 4 WITNESSES: INVENTOR Patented Aug. 17, 1943ELECTRIC DISCHARGE APPARATUS Harold C. Jenks, Wilkinsburg,

Pa., assignor to Westinghouse Electric & Manufacturing Company, EastPittsburgh, Pa.,

Pennsylvania a corporation of Application August 11, 1939, Serial No.289,557

. 8 Claims. My invention relates to electric discharge sysparatus.

In resistance spot and seam welding, it is often desirable to heat thematerial to be welded just before the fusing current is applied and toanneal the weld just after the material has been fused. Weldingapparatus incorporating preheating or annealing functions constructed inaccordance with the teachings of the prior art is, in general,relatively complicated. The principal difficulty arises from the factthat to produce a satisfactory weld the time during which weldingcurrent flows should in general be measured out precisely. Theattainment of this desideratum resultsin a relatively involved systemand the additional requirements of reduced current flow for additionaltime periods before and after, the flow of the actual welding currentadds to its complexity.

It is, accordingly, an object of my invention to provide a weldingarrangement of simple structure with which it shall be possible to heatthe material to be welded before the actual welding current is suppliedor to anneal the fused material after the welding current has beensupplied.

Another object of my invention is to provide welding apparatus of simplestructure with which it shall be possible to satisfactorily anneal aweld,

A further object of my invention is to provide welding apparatus ofsimple and tractable structure with which it shall be possible topreheat the material to be welded immediately before it is fused andanneal the weld immediately after it has been produced.

More generally stated, it is an object of my invention to provide anarrangement 01 simple structure for supplying power from a source to aload of the type that requires current in contiguous trains of impulsesof precisely predetermined length but of different amplitude.

According to my invention, I provide a welding arrangement which isenergized from an alternating current source and which operates tosupply welding current during discrete half cycles of the source. Theflow of rent through the material to be welded is initiated at instantsin the half periods of the source that occur substantially earlier thanthe normal current zero for'the power factor of the particular loadinvolved. When the flow of actual welding current initiated in thismanner is interrupted, the welding transformer remains magnetized andthe reduced current flow produced by reason of the decay of flux in thetransformer is used foranterns and has particular relation to weldingapnealing purposes. The magnitude of the residual current may be variedby premagnetizing the core of the welding transformer to any desiredextent. In the preferred practice of my invention, the residual currentis used for annealing purposes. It is apparent, however, that thecurrent may also be used for preheating purposes. In such a case, thewelding current for any weld is supplied immediately after the residualcurrent has ceased to flow and the material to be Welded is advanced toa position to receive the residual current which flows by reason of thejust preceding magnetization of the transformer. This object may, ofcourse, be accomplished by properly synchronizing the supply of Weldingcurrent with the movement of the material to be Welded in engagementwith the welding electrodes.

In accordance with another aspect of my invention, I provide anarrangement in which the usual electric discharge valves are interposedbe tween an alternating current source and the material to be welded,The valves are rendered conductive by potential supplied through a phaseshift network. The latter incorporates a pair of voltage dividerswhichdetermine the instants in the half periods of the source when theenergizing potentials are supplied through the network, One of thevoltage dividers is set to render the valves conductive at instants inthe half periods of the source corresponding to annealing and preheatingcurrent and the other is set for welding current. The former voltagedivider is coupled to the valve means for predetermined intervals oftime before and after the interval during which the welding currentflows. The other is coupled to the valve meansduring the welding currentinterval. 7

The novel features that I consider character istic of my invention areset forth with particularity in the apended claims. The inventionitself, however, both as to its organization and its method ofoperation, together with additional objects and advantages thereof, willbest be understood from the following description of specificembodiments when read in connection with the accompanying drawings, inwhich:

Figure 1 is a diagrammatic view showing a preferred embodiment of myinvention,

Fig. 2 is a graph illustrating the operation of Fig. l,

Figs. 3 and 4 together constitute a diagrammatic view showing amodification of my invenrent supply circuit ode gaseous type.

in a copending application Serial No. 206,643,

filed May '1, 1938, to J. W. Dawson and assigned to the assignee of thepresent application. It comprises a welding transformer 1 supplied fromsource 9 of alternating current, which may be of the usual commercial 60cycle type. The secondary ll of the transformer 1 is connected across apair of welding electrodes l3 which engage the material l tobe welded.The primary H of the transformer 1 is supplied from the source 9 throughan ignitron tube l9. The latter comprises an anode 2|, a mercury pool,cathode 23 and an ignition electrode 25. The transformer 1 is suppliedwith premagnetizing current from a rectifier 21, which is connectedacross an auxiliary winding 29 on the core 3| through an adjustingrheostat 33 and an interrupting switch 35.

The polarity of the direct current supplied to the auxiliary winding 29should in general be the same as the polarity of the current suppliedthrough the ignitron l9. However, under certain circumstances, thepremagnetizing current may be of the opposite polarity and in thepreferred practice of my invention the premagnetizing cur- 21, 33incorporates a reversing switch and a voltagedivider with a center tapso that current of either polarity may be supplied to the auxiliaryWinding 29. The. efiect of premagnetizing current of the same polarityas that supplied through the ignitron I9 is to increase themagnetization of the core beyond that produced by the current flowthrough the ignitron and thus to increase the residual current producedby the decay of the flux. Current of the opposite polarity, of course,has the converse efiect.

The ignitron I9 is controlled from an auxiliary electric discharge valve31 of the hot cath- The latter is provided with an anode 39, a cathode4| and a control electrode 43. Control potential is supplied to theauxiliary valve 31 from a peaking transformer 45, the primary 41 ofwhich is connected across the source 9 through a rheostat 49 whichfunctions to determine the phase of the peaks supplied by thetransformer relative to the potential of the source.

The secondary 5| of the peaking transformer 45 is connected between thecontrol electrode 93 and the cathode Bl of the auxiliary valve 31through the cathode 23 and the ignition electrode 25 on the ignitron l9.The secondary circuit of the peaking transformer 45 thus extends fromthe upper terminal of the winding 5| through a conductor 53, a conductor55, a conductor 51, the cathode 23 and the ignition electrode 250i theignitron I9, a conductor 59, the cathode 4| of the auxiliary valve 31,the control electrode 43 of the auxiliary valve, a resistor 6|,

. a network 63 consisting of a resistor 65 shunted by a capacitor 51 tothe lower terminal of the winding 5|. Anode potential is supplied to theauxiliary valve 31 from a capacitor 69 which is charged from the mainsource 9 through a rectifier 1| just prior to the initiation of awelding operation.

To produce a weld, the electrodes |3 are engaged with the material i5and a startingcircuit controller 13 which may be a push button or a footswitch is operated in one sense. By this operation, the capacitor 59 isconnected to the rectifier 1| and charged. After this, the conv theswitch 95 troller is operated in the opposite sense and the capacitor 69is now title! and connected to the anode 39 of the auxiliary valve 31.The controller 13 is coupled to in such manner that the operation in thefirst sense does not afiect the switch but the operation in the lattersense opens the switch disconnecting the rectifier 21 from the auxiliarywinding 29.

At an instant predetermined by the setting of the rheostat 49 in theprimary circuit of the peaking transformer 45, the auxiliary valve 31 isrendered conductive and the capacitor 99 is discharged in a circuitextending from its righthand plate 15 through the contacts 11 and 19 ofthe controller 13, the anode 39 and cathode 4| of the auxiliary valve31, the conductor 59, the ignition electrode andcathode 23 of theignitron valve i9, the conductor 51, the conductor 55, the conductor 53to the left-hand plate 8| of the capacitor. The ignitron is now renderedconductive and current flows through the welding transformer 1 and thematerial |5 to be welded.

'rent may be set at The rheostat 49 in series with the primary 41 of thepeaking transformer 45 is so set that the current flow through theignitron I9, is initiated at an instant substantially earlier in thehalf period the source than the instant of normal current zero. When thecurrent flow through the ignitron I9 is interrupted, the weldingtransformer 1 is magnetized and residual current flows by reason of thedecay of the flux in the transformer core 3| and generates heat foranealing the weld.

In addition to the current produced by reason of the decay of themagnetization arising from the current flow through the ignitron l9,there is also current flow by reason of the premagnetization. The lattermay be adjusted at will by properly setting the magnitude of the directcurrent which is supplied through the auxiliary winding 29. By properlyadjusting the 'premagnetization, the magnitude of the annealing curthemost The operation of the apparatus shown in Fig. l is illustrated inFig. 2. In the latter view, current and potential are plotted verticallyand time horizontally. The light lined sine wave 83 represents the'potential supplied from the source 9. The medium sine wave 85 representsthe steady state current which would flow through the welding load wereit permanently connected to the source 9. The phase lag indicatedbetween the potential and the current corresponds to the power factor ofthe load. The heavy curve 81 indicates the actual current flow throughthe material to be welded. It is to be noted that the current isinitiated at a point 99 substantially earlier in the half cycle than thepoint 9| at which the normal current zero occurs. At the point 93 wherethe heavy curve 81 cuts the abscissa 95, the current flow through thevalve l9 ceases. However, because the welding transformer 1 ismagnetized, current flow through the material 15 to be welded continuesin the oppodisconnected from the recpropitious value.

- trode I45.

annealing current is to be smaller than that available by reason of theflux arising from the main valve current, the premagnetization may be inthe opposite sense to the magnetization produced by the valve current.

In the apparatus shown in Figs. 3 and 4, current is supplied to theprimary 99 of a welding transformer I M from the source 9 through a pairof ignitrons I03 and I05 connected in antiparallel. Each of theignitrons has an anode I01, a cathode I09 and an ignition electrode III.Ignition current is supplied to the ignitrons I03 and I05 through timingvalves H3 and H5 respectively, and heat control valves H1 and H9respectively; a timing valve and a heat control valve being connected inseries with the ignition electrode and the cathode of each of theignitrons. The timing valves H3 and H5 each cornprise an anode I2I, ahot cathode I23 and a control electrode I25 and are preferably of thearc- Iike discharge type. The heat control valves are also of thearc-like type and each comprises an anode I21, a hot cathode I29 and acontrol elec-= trode I3I.

The conductivity of the timing valves IE3 and H5 is controlled in theusual manner from a timing system I32 incorporating a start valve I33,which supplies current to charge a timing capacity I through a rheostatI31, and a stop valve I39 which renders the start valve I33nonconductive when the capacitor I35 attains a predetermined charge. Thestart valve i33 is of the arc-like discharge type and comprises an anodeI4I, a hot cathode I43 and a control elec- The stop valve I39 is also ofthe arclike type and in addition to a hot cathode I41 comprises an anodeI49 and a control electrode I5I.

The conductivity of the heat control valves H1 and H9 is controlled froma phase shift network I53 of the usual structure comprising a reactorI55 and a resistor I51 connected in series with each other across thesecondary I59 of an auxiliary transformer IBI supplied from the I source9. Between the'reactor I55 and the resistor I51 a pair of parallelconnected voltage dividers I63 and I65 are interposed. The ignitionimpulses are applied between the control electrodes I3i and the cathodesI29 of the heat control valves I I1 and H9 through a pair of controltransformers I61 and I69, the primaries HI and I13 of which are suppliedwith potential from the phase shift network I53. The intermediate tapI15 of the secondary .I59 of the auxiliary transformer I6! is connectedto the adjustable tap I11 f a resistor I19 interconnecting the lowerterminals of the primaries Ill and I13. The adjustable tap I8I of one ofthe voltage dividers I63 is connected to the conductor I83 connectingthe upper terminals of the primaries HI and I13 of the controltransformers I61 and I69 through a resistor I85. The resistor I85 may beshort circuited by a conductor I81 extending from the adjustable tap 189of the other voltage divider I65 whenthe normally open movable contactorI9I of a relay I93 controlled from the timing system I32 is energized.

The former voltage divider I63 is set so that the potential suppliedthrough it renders the heat control valves H1 and H9 conductive atinstants late in the haltperi'ods of the source corresponding to thepreheating and annealing current desired. In practice, the heat controland annealing current may be the same if a proper magnitude suitable forboth purposes is selected. The other voltage divider I65 is set so thatthe heat control valves H1 and I I 9 are rendered conductive at instantsearly in the half periods of the source corresponding to the weldingcurrent required. The connection of the voltage dividers I63 and I65 inthe control circuit to the heat control valves is controlled from a pairof auxiliary timing systems I95 and I91, each of which incorporates avalve I99 and 20I respectively controlled from a timing capacitor 203and 205 respectively in its control circuit.

To control the start valve I33, 9. control valve 201 of the arc-liketype comprising an anode 209, a hot cathode 2H and a control electrode2I3 is provided. The control valve is supplied with anode-cathodepotential from a transformer 2I5 energized from the main source 9. Aphase shift network 2| 1 comprising a variable resistor 2I9 and acapacitor .22I is connected across the secondary 223 of thetransformer..

The control electrode 2| 3 of the valve 201 is connected to the junctionpoint 225 of the variable resistor 2I9 and capacitor 22I and the'cathode2 to the intermediate tap 221 of the secondary. The anode 209 of thecontrol valve 201 is connected through a current limiting resistor 229and the primary 23I of a control transformer 233 to the upper terminalof the secondary 223 of the supply transformer. After the main switch(not shown) for the plant is closed the control valve 201 is renderedconductive during alternate half cycles at instants in the half periodswhich are determined by the setting of the phase shift network 261.

To initiate a welding operation, a circuit con; troller 235 such as afoot switch or a push button, is closed and a starting relay 231 isenergized. An intermediate contactor 239 of the relay 231 closes andconnects the anodes HI and I49 of the start and stop valves I33 and I39respectively to the positive terminal 24I of a direct current supplysource 243. At the same time another contactor 245 closes and connectsthe secondary 241 of the control transformer 233 across a resistor 249in the control circuit of the start valve I33. When the control valve201 is next rendered conductive, a potential impulse is induced in thesecondary 241 of the control transformer 233 and potential is suppliedto the control electrode I45 of the start valve I33 in a circuit whichextends from the upper terminal of the resistor 249 now connectedthrough the movable contactor 245 to the secondary 241 of the controltransformer 233, through a grid resistor 25I to the control electrodeI45 of the start valve I33, the cathode I43 of the start valve, arheostat 253, a resistor 255, a conductor 251, a biasing source 259 tothe lower terminal of the resistor. The potential thus impressed in thecontrol circuit renders the start valve I33 conductive, current issupplied in a circuit. extending from the positive terminal 24I of therectifier 243 through the movable contactor 239 of the starting relay231, the anode MI and the cathode I43 of the valve I33, the rheostatI31, the timing capacitor I35 to the negative terminal 26I of therectifier 243, and the timing capacitor I35 is charged. Current is alsosupplied through the start valve I33 to a voltage divider 253 which isconnected between the cathode I43 of the start valve and the negativeterminal 26I of the rectifier 243.

The adjustable tap 263 of the latter voltage divider 253 is connected tothe intermediate tap 265 of the secondary 261 of a transformer 269, theterminal taps of which are connected to the control electrodes I25 ofthe timing valves H3 and H through suitable grid resistors 21I and 213.The cathodes I23 of the timing valves H3 and I I5 are connected throughthe ignition electrodes III and the cathodes I09 of the associatedignitrons I03 and I05, corresponding conductors 215 and 211 andresistors 219 and 28l and a common conductor 283 to an intermediate tap285 of a voltage divider 291 interconnecting the terminals 24I and 26Iof the rectifier 243. Since the voltage divider 253 in series with thestart valve I33 is connected to the negative terminal 26I of therectifier 243, the circuit between the control electrodes I25 and thecathodes I23 of the timing valves H3 and H5 is thus closed. Therefore,when current is supplied through the latter voltage divider 253, thetiming valves H3 and H5 are at once rendered conductive. Thecorresponding heat control valves H1 and I I9 are initiallynon-conductive and current flows through each of the'timing valves I I3and H5 in circuits including resistors 289 and 29l, respectively, whichshunt the corresponding heat control valves H1 and H9. The resistors 289and 29I are so large that the current supplied in the ignition circuitsof the corresponding ignitrons I03 and I05 is insufficient to render theignitrons conductive. I03 the circuit extends from the lower terminal ofthe main source 9 through a line conductor 293, a conductor 295, aconductor 291, a resistor 299, the upper movable contactor 30I of thestarting relay 231, a conductor 303, the shunting resistor 289, theanode I2I and the cathode I23 of the corresponding timing valve H3, aresistor 305, the ignition electrode Ill and the cathode I09 of theignitron I03, a conductor 301, a conductor 309, the primary 99 of thewelding transformer IN, a line conductor 3II to the upper terminal ofthe source 9. The circuit for the other ignitron is similar.

The. heat control valves -first supplied with potential from the voltagedivider I63 the variable tap I8I of which is connected to the controltransformers I61 and I69 through the resistor I85. Therefore, at aninstant predetermined by the setting of the voltage divider I63, theheat control valves are rendered conductive and short circuit theirassociated shunting resistors 289 and HI, respectively. Suflicientcurrent is now transmitted through the ignitron electrodes III andcathodes I09 of the corresponding ignitrons I03 and I05 and the latterare each in its turn rendered conductive at instants in the half periodsof the source corresponding to the setting of the voltage divider I63,and supply current to the material I5. The voltage divider I63 is so setthat the current supplied is too small for welding purposes butsufiicient to preheat the material to be welded.

For the left-hand ignitron capacitor 205, the conductor 311 to thenegative terminal 26I of the direct-current supply. The capacitors 203and 205 are, therefore, charged at a rate predetermined by theirassociated rheo- H1 and us are at The timing capacitors 203 and 205 ofthe two auxiliary timing circuits I95 and I91 are each connected incircuit with the voltage divider 253 in series with the start valve I33.The circuit'for one of the capacitors 203 extends from the upperterminal of the voltage divider 253 through a rheostat 3I3, a resistor3I5, the capacitor 203, a conductor 3" to the negative terminal 26I ofthe direct-current supply 243 which is, in turn, connected to the lowerterminal of the voltage divider 253. The other circuit extends from theupper terminal of the voltage divider through a second rheostat 3I9. theother stats 3I3 and 3I9, respectively.

The potentials supplied by the two are impressed in the control circuitsof responding auxiliary timing valves I99 and 20L The circuit for thefirst capacitor 203 extends from its upper plate 32I through a gridresistor 323, the control electrode 325 of the corresponding timingvalve I99, the cathode 321 of the valve, a conductor 329, a conductor33I, the intermediate tap 285 of the voltage divider 201 energized fromthe direct-current supply 243, the lower portion of the voltage dividerto the lower plate 333 of the capacitor 203. The'other capacitor 205 issimilarly connected to its corresponding valve 20I,

The rate of charging of the two capacitors is such that the valve I99associated with the first capacitor 203 is rendered conductive at aninstant corresponding to the time at which the preheating interval is toterminate. Current then flows in a circuit extending from the positiveterminal 335 of the direct-current supply 331 provided for the auxiliarytiming valves I99 and 20I through closed contactor 338 of the startingrelay 231, a conductor 339, the exciting coil 34I of the relay I93controlling the conneccapacitors the cortion of the heat control voltagedividers I63 and I65, the movable contactor 343 of a relay 345controlled from the other auxiliary timing valve 20I, the anode 341 andthe cathode 321 of the first timing valve' I99, the conductor 329 to thenegative terminal 349 of the direct current supply. The relay I93controlling the voltage dividers I63 and I65 is energized and thevoltage divider I65 replaces the other divider I63 in the primarycircuits of the control transformers I61 and I69. The heat controlvalves H1 and H9 are now rendered conductive at instants in the halfperiods predetermined by the setting of the voltage divider I65. Thelatter is so set that the resultant current supplied to the material I5is sufficient for welding.

After the welding current has been transmitted for a predeterminednumber of half periods, the timing capacitor 205 in the auxiliary timingcircuit I91 acquires sufilcient positive potential to render theassociated valve 20I conductive. Current now flows in a circuitextending from the positive terminal 335 of .the rectifier 331 throughthe contactor 338, the conductor 339, the exciting coil 35I of the relay345 which maintains the circuit of the other auxiliary timing valve I99closed, the anode 353 and cathode 355' of the auxiliary timing valve20I, the conductor 329 to the negative terminal 349,

The relay 345 is now energized and opens the anode circuit, of the otherauxiliary timing valve I99 causing the relay I93 controlling theconnection of the voltage dividers I63 and I65 to be deenergized. Thewelding voltage divider I65 is now disconnected from the controlcircuits of the heat control valves H1 and H9 and the other voltagedivider I63 again becomes effective. The current which now flows throughthe material I5 is the same as the preheating current and the setting ofthe voltage divider is such that this current is sufficient forannealing Pu poses.

The annealing current continues to flow until the timing capacitor I35in series with the start tube I33 becomes charged to a predeterminedpotential. The latter capacitor is connected between the controlelectrode II and the cathode I41 of the stop valve I49 and when itattains the present potential, the stop valve I49 is rendered conductiveand reduces the anode-cathode potential across the start valve I 3| tosuch an extent that the latter becomes non-conductive. Current flowthrough the voltage divider 253 in circuit with the start valve nowceases and, therefore, the corresponding timing valves H3 and H5 in theignition circuits of the ignitrons I03 and I05 are renderednon-conductive. Current flow through the material I5 to be Welded,therefore, ceases.

The operation of the system is illustrated in Fig.5. In this viewpotential and current are plotted vertically and time is plottedhorizontally. The full sinusoidal curve 354 represents the sourcepotential, The small circles 356 represent the position of the powerfactor angle, i. e., normal current-zero points, The first two smallhalf waves 35! from the left represent the preheating current fiow. Itis to be noted that each of the half waves is initiated at an instant359 in the corresponding half cycles substantially later than thatcorresponding to the power factor angle. The larger half waves 36l inthe center represent the welding current. This current, it is to benoted, is initiated at instances 363 immediately following thosecorresponding to'the power factor points 356. The two small half waves365 on the right represent the annealing current. The latter are of thesame amplitude as the preheating current half waves.

It is to be noted that in the system illustrated in Fig. 5, thepreheating and annealing half waves are equal in number. Of course, thisneed not necessarily be the case. The length of time during which thepreheating and annealing current flows is set by the rheostats 3I3 and3I9 in series with the capacitors in the control circuits of theauxiliary timing valves I99 and MI and assume any desired values.

such that the decay of the flux in said reactiv means after said valvemeans is rendered nonconductive causes the flow of suflicient currentthrough said material to anneal it.

3. For use in supplying power from a source of periodically pulsatingpotential to a load the combination comprising valve mean interposedbetween said source and said load, a phase shift network for supplyingpotential impulses to render said valve means conductive and including afirst voltage divider for determining the phase of said potentialimpulses supplied by said network relative to the potential of saidsource and a second voltage divider for determining the phase of saidpotential impulses supplied by said network relative to the potential ofsaid source,said dividers being set so that said network suppliespotentials having different phases for each of them, means for couplingsaid first divider to said valve means for a predetermined interval oftime thereby to initiated the conductivity of said valve means duringsaid interval at instants in the periods of said source that correspondto the phase at which said first divider is set, and means for couplingsaid second divider to said valve means for another predeterminedinterval of time thereby to initiate the conductivity of said valvemeans dur- Although I have shown and described certain specificembodiments of my invention, I am fully aware that many modificationsthereof are possible. My invention, therefore, is not to be restrictedexcept insofar as is necessitated by the prior art and by the spirit ofthe appended claims.

I claim as my invention:

1. For use in supplying power for welding a material from a source ofcurrentthe combination comprising reactive means having a magnetizablecore interposed between said source and said material, valve means forcontrolling the supply of welding current through said reactive means tosaid material and means for rendering said valve means conductive tosupply welding current to said material for an interval of time suchthat when current flows through said reactive means is interrupted thedecay of flux in said reactive means causes the flow of sufilcientcurrent through said material to anneal it.

2. For use in supplying power for welding a material from a source ofalternating current the combination comprising reactive means having amagnetizable core interposed between said source and said material,valve means permitting the flow of only a half cycle of current fromsaid source for controlling the supply of welding current through saidreactive means to said material and means for initiating theconductivity of said valve means at an instant in a half period of saidsource that is earlier than the normal current zero instant by apredetermined amount ing said other interval at instants in the periodsoiv source that correspond to the phase at which said second divider isset.

4. For use in supplying power from a source of periodically pulsatingpotential to a load the combination comprising valve means interposedbetween said source and said load, a phase shift network for supplyingpotential impulses to render said valve means conductive and including afirst voltage divider for determining the phase of said potentialimpulses supplied by said network relative to the potential of saidsource and a second voltage divider for determining the phase of saidpotential impulsessupplied by said network relative to the'potential 01'said source, said first divider being so set that the potential impulsesto render said valve means conductive are supplied through it atinstants late in the periods of said source and said second dividerbeing so set that the potential impulses to render said valve meansconductive are supplied through it early in the periods of said source,means for coupling said first divider to said valve means during twopredetermined intervals of time separated by an intermediate interval oftime thereby to initiate the conductivity of said valve means duringsaid two intervals at instants late in the periods of said source, andmeans for coupling said second divider to said valve means during saidintermediate interval thereby to initiate the conductivity of said valvemeans during said intermediate interval at instants early in the periods01 said source.

v 5. For use in supplying power for welding a material from a source ofcurrent the combination comprising reactive means having a magnetizablecore interposed between said source and said material, valve means forcontrolling the supply of welding current through said reactive means tosaid material, means for rendering said valve means conductive to supplywelding current to said material for an interval of time such that whencurrent flow through said reactive means is interrupted the decay offlux in said reactive means causes the flow of sufficient currentthrough said material to anneal it, means for supplying direct currentto said core to premagnetize said core, means for varying the magnitudeof direct current to vary the magnitude of said annealing current, andmeans for interrupting the supply of direct current when said valvemeans is rendered conductive.

6. For use in supplying power from a source of periodically pulsatingpotential to a load, the I combination comprising valve means interposedbetween said source and said load, a phase shift network for producingpotential impulses ofv the same periodicity as said source potential andincluding a pair of voltage dividers for'determining the phase of to thesource potential, said dividers being set so that the phase of thepotential impulses produced through the first of said dividers isdifierent from the phase of the potential impulses produced through thesecond divider, and means for coupling said network to said valve meansfor supplying potential impulses through one of said dividers to renderthe valve means conductive at instants in the periods of said sourcecorresponding to the phase of the potential impulses supplied theretoand including means for selecting the one of said dividers through whichthe potential impulses to render said valve means conductive aresupplied.

7. For use insupplying power from a source of periodically pulsatingpotentialto a load, the combination comprising valve means interposedbetween said source and said load, a phase shift network for producingpotential impulses of the same periodicity as said source potential andincluding a pair of voltage dividers for determining the phase of saidpotential impulses relative to'said source potential, said dividersbeing'set so that the phase of the potential impulses prosaid potentialimpulses relative duced through the first of said dividers is diflerentfrom the phase of the potential impulses produced through the seconddivider, means for coupling said network to said valve means to supplypotential impulses through the first divider for rendering the valvemeans conductive, and switch means for changing the coupling of saidvnetwork to said valve means to supply potential impulses through thesecond divider for rendering the valve means conductive.

8. In combination, an electric discharge valve of the arc-like typehaving a pair of principal electrodes and a control member, a source ofperiodically pulsating potential connected across said principalelectrodes, a phase shift network for producing two sets of potentialimpulses each having a difierent phase relative to said source, saidnetwork including a first voltage divider for determining the phase ofthe potential impulses of the first of said sets of impulses and asecond voltage divider for determining the phase of the potentialimpulses of the second set, means for connecting said network to impresssaid first set of potential impulses between one of'said principalelectrodes and said control member to render said valve conductive atinstants in the periods of said source that correspond to the phase ofthe potential impulses so impressed, and switch means for changing theconnection of said network to impress said second set of potentialimpulses between said one electrode and said control member to rendersaidlvalve conductive at instants in the periods of said sourcepotential that correspond to the phase of the potential impulses of saidsecond set.

HAROLD C. JENKS.

